1. Field of the Invention
This invention relates to an aiming point locating system and, more particularly to a system for identifying the point on a cockpit display, or the like, viewed by a pilot.
2. Description of the Prior Art
A number of visual responsive systems have been proposed which incorporate emitters and sensors mounted either on the pilot's helmet or in the cockpit so that the line of sight of the pilot can be tracked in order to preclude the necessity of identifying a particular situs by hand. One such system is disclosed in U.S. Pat. No. 3,971,412 issued Nov. 4, 1975 to Stoutmeyer et al for ADVANCED HELMET TRACKER USING LATERAL PHOTODETECTION AND LIGHT-EMITTING DIODES. In this system two light emitters are mounted on the helmet of the pilot while two photodetectors are mounted at spaced locations within the cockpit of the aircraft. The emitters are positioned such that they define a line parallel to the pilot's line of sight and the pilot's line of sight is determined by measuring the intersection of the planes formed by each emitter together with the two detectors. Ideally the system has four light emitting diodes, two of which are mounted on each side of the pilot's helmet. Four detectors mounted in the cockpit are directed toward the pilot's helmet so as to have intersecting fields of view no matter the position of the pilot's head. A problem with this particular system is that at least two emitters must be mounted on the pilot's helmet which add to overall helmet weight and increase the complexity of electrical connections and the like.
Another similar system is disclosed in U.S. Pat. No. 3,678,283 issued July 18, 1972 to LaBaw for RADIATION SENSITIVE OPTICAL TRACKER. A photodetector assembly capable of identifying location is positioned on the helmet of the pilot while two light emitters are mounted in the cockpit. This apparatus serves to measure the amount of roll of the pilot's helmet, a second assembly consisting of a light emitter disposed on the helmet of the pilot together with another photodiode positioned in the cockpit measures the angle of the pilot's sight in the remaining plane to measure the location of the helmet. A disadvantage of this particular system is that two emitters are required to obtain an electrical output signal indicating the pilot's line of sight. Another disadvantage of this particular system is that the photodiodes required for operation are relatively expensive and complicated to manufacture.
Other oculometer systems which are capable of producing electrical signals indicative of the direction an operator is looking include U.S. Pat. No. 4,109,145 issued Aug. 22, 1978 to Graf for APPARATUS BEING CONTROLLED BY MOVEMENT OF THE EYE.
Another prior art system which may be of interest is that disclosed in U.S. patent application Ser. No. 864,956 filed Dec. 27, 1977 by Brienza et al for REMOTE OPTICAL DISPLAY DESIGNATOR assigned to the same assignee as the present invention. This system employs a remote source of energy in a handheld or helmet mounted unit to generate an identifying beam on the faceplate of a CRT through which an image is being displayed. The diffusing medium deposited on the rear of the CRT faceplate scatters the incident beam to orthogonal pairs of photodetectors located adjacent the edges of the faceplate. A disadvantage of this system is that the display device must be of the type which includes a diffusing medium for scattering the impinging energy from the source. Accordingly, the system does not work well with display devices which do not include a diffusing medium, i.e. plasma panels, some liquid crystal displays, light emitting diode displays, and the like, in that the electromagnetic energy reaching the photo pickups would not be sufficient for proper operation. In addition, many cathode ray tubes have curved faceplates and scattered light, particularly from points near the edges of the CRT, must travel through the entire length of this curved pathway, often by secondary scatter, to the photo pickups adjacent the edges of the faceplate. Accordingly, the inherent attenuation significantly reduces the intensity of the energy finally reaching the photo pickups.